A typical pre-treatment part of a water treatment plant or a desalination plant consists of settling tanks, sand filters, strainers & micron filters. The turbidity level is brought down to the acceptable range in various stages using progressively lower/finer filtration rating equipment, before feeding it to high pressure pumps and then in turn to core filtration system like RO plant.
Basket strainers & cartridge filters
Basket strainers/filters are commonly used to achieve primary filtration of feed water. These filters generally offer degree of filtration of the order of 100 to 400 microns in stages/series. The basket strainers are further classified depending on the direction of flow viz. in to out or out to in. they are many times provided with mechanical brush or backwash arrangement to clean in situ. Basket strainers are followed by Micron filters. In water treatment industry Cartridge filter are widely used owing to various operational and maintenance advantages. The cartridge filters are generally of 5 micron rating having multiple cartridges housed inside a pressure vessel with various sealing arrangements. The filters thus ensure long life of costly membranes and high pressure pumps. Various water conditioning & membrane protecting chemicals and additives are also added to water in this stage before the water enters membranes. The cartridges over a period; get clogged with dirt and obstructs the flow causing a pressure drop across the housing. At this time they are removed and replaced with the new ones unlike backwashing in strainers. For continuous running plant a duplex arrangement with two vessels in parallel with interconnecting piping is used. Also many inline strainers like Y, T type strainer are used at the suction of acid/alkali pumps to avoid intrusion of any foreign particle in the line. These inline strainers are generally of 200 -400 micron rating.
MOC for strainers & cartridge filters
Water when dosed with various conditioning chemicals and additives becomes a corrosive solution. In order to avoid any corrosion in these equipment MS rubber lined or stainless steel vessel has been traditionally used in such housings. Owing to high TDS of sea water, desalination plants, have to use exotic SS material like duplex or super duplex steel with high chromium contents or MS rubber lined vessels. Duplex steel materials are extremely costly, scarcely available and needs highly trained workman to do fabrication while, MS rubber lined vessels come with disadvantages of External corrosion, de-bonding of rubber lining and other maintenance related issues. GRP/FRP & PP material is widely used in water treatment industry for various small components to big equipment like tanks and pressure vessel where high level of corrosion resistance is required. GRP pipes are now readily accepted for conveying water and is a popular choice in desalination plants across the globe.
DM. ENGINEERING CO.